Flexible active matrix display backplane and method

ABSTRACT

An active matrix display backplane is formed by annealing a flexible dielectric substrate, and then forming one or more thin-film-transistors (TFTs), one or more pixel electrodes, and an interconnect on a surface of the annealed substrate. The interconnect includes individual, spaced apart electrodes that are electrically coupled to one another. One of the interconnect electrodes is electrically coupled to a TFT, and the other interconnect electrode is electrically coupled to the pixel electrode, to thereby electrically interconnect the TFT and the pixel electrode.

FIELD OF THE INVENTION

The present invention generally relates to active matrix displays and,more particularly, to a method of forming thin-film-transistor (TFT)displays backplane directly on a flexible substrate.

BACKGROUND

Presently, there is an increasing interest in developing flexible AM(active matrix) displays for both military and commercial applications.This is at least partially because active matrix display technologyprovides the potential to realize relatively rugged, full color,lightweight, low power, and low cost flexible displays. Currently, mostactive matrix displays use rigid glass substrates. Many of these rigidactive matrix displays have been, and continue to be, in commercial usein a variety of applications and sizes. For example, relatively smallsize (e.g., ˜2-inch diagonal) displays have been used in some digitalcameras and mobile phones. Relatively large size (e.g., >˜15-inchdiagonal) active matrix displays have been used in various otherconsumer products including, for example, personal computers (PCs) andtelevisions (TVs).

Although rigid active matrix displays are generally reliable and robust,flexible active matrix displays offer certain potential advantages. Forexample, flexible active matrix displays may enable many unique displayapplications, due to the inherent ruggedness and unique form factors ofconformability and rollability during use, transportation, and storage.Flexible displays may also be amenable to roll-to-roll manufacturingprocesses, which may provide significant reduction in manufacturingcosts.

Unfortunately, the current processes for fabricating active matrixdisplays typically are not adequate for the fabrication of active matrixdisplays using flexible plastic substrates. This is due, at least inpart, to the flexible substrate having a CTE (coefficient of thermalexpansion) that is significantly larger (˜20 ppm versus ˜3 ppm) than thetypical thin films that are used to form thin-film-transistors (TFTs) onthe substrate. As a result, thermal stresses may arise, which can leadto curling and warping of the flexible substrate during processing. Inmost instances, it is not be possible to conduct the variousphotolithography operations on curled and warped substrates, therebymaking it rather difficult, if not impossible, to process the substrateto completion. Moreover, the flexible substrates may shrink duringvarious TFT processing operations, resulting in dimensional instabilitythat may make layer to layer alignment fairly difficult.

Hence, there is a need for a method of fabricating an active matrixdisplay backplane directly on a flexible substrate that does not causesignificant thermal stresses in the substrate during TFT processingand/or is relatively dimensionally stable. The present inventionaddresses one or more of these needs.

BRIEF SUMMARY

The present invention provides a TFT display backplane in which the TFTsand pixel electrodes are formed directly on a flexible substrate. In oneembodiment, and by way of example only, a method of forming an activematrix display backplane on a flexible dielectric substrate includesforming a gate layer on a surface of the flexible dielectric substrate,forming a gate dielectric layer over the gate layer, forming anamorphous silicon (a-Si) layer over at least a portion of the gatedielectric layer, forming an inter-metal dielectric layer over the a-Silayer, selectively removing portions of the inter-metal dielectric layerover the a-Si layer, selectively removing portions of the inter-metaldielectric layer to thereby expose at least a source contact region anda drain contact region on the a-Si layer, forming a source contact inthe source contact region, and forming a drain contact in the draincontact region.

In another exemplary embodiment, a method of electricallyinterconnecting a thin-film-transistor (TFT) and a pixel electrodeformed on a substrate includes forming a conductive material layer onthe substrate, forming an interconnect contact and a pixel electrodecontact on the conductive material layer, electrically coupling the TFTto the interconnect contact, and electrically coupling the pixelelectrode to the pixel electrode contact.

In yet another exemplary embodiment, an active matrix display backplaneincludes an annealed flexible dielectric substrate, athin-film-transistor (TFT), a pixel electrode, and an interconnect. Theannealed flexible dielectric substrate has at least a first surface anda second surface. The TFT is formed on the annealed flexible dielectricsubstrate first surface. The pixel electrode is formed on the annealedflexible dielectric substrate first surface. The interconnect is formedon the annealed flexible dielectric substrate, and includes a conductor,an interconnect contact, and a pixel electrode contact. The interconnectcontact and pixel electrode contact are formed on the conductor. Theinterconnect contact is electrically coupled to the TFT, and the pixelcontact is electrically coupled to the pixel electrode.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will hereinafter be described in conjunction withthe following drawing figures, wherein like numerals denote likeelements, and wherein:

FIG. 1 is a schematic diagram of an exemplary embodiment of an activematrix display backplane;

FIG. 2 is a cross section view of a portion of the backplane shown inFIG. 1;

FIGS. 3-11 are cross section views of the backplane shown in FIG. 1,illustrating the various exemplary methodological steps that are used tomake the backplane;

FIG. 12 is a cross section view of an exemplary embodiment of a portionof an active matrix OLED (organic light emitting diode) displayfabricated using the flexible active matrix backplane of FIG. 11; and

FIG. 13 is a cross section view of a portion of the backplane shown inFIG. 1 according to an alternative embodiment of the present invention.

DETAILED DESCRIPTION

The following detailed description of the invention is merely exemplaryin nature and is not intended to limit the invention or the applicationand uses of the invention. Furthermore, there is no intention to bebound by any theory presented in the preceding background of theinvention or the following detailed description of the invention. Inthis regard, the display backplane described herein includes an array ofthin-film transistors associated with each display pixel, which are usedto control each pixel. However, the transistor may also be used in anyother active matrix display devices such as organic light emittingdisplays and electrophoretic displays, for example.

A schematic diagram of an exemplary embodiment of an active matrixdisplay backplane 100 is shown in FIG. 1, and includes a plurality ofgate bus lines 102, a plurality of data bus lines 104, a gate drivercircuit 106, a data driver circuit 108, a plurality ofthin-film-transistors (TFTs) 112, and a plurality of pixel electrodes114. The gate bus lines 102 and data bus lines 104 are each connected tothe gate driver circuit 106 and the data driver circuit 108,respectively, and receive gate drive signals and input data signalvoltages supplied respectively therefrom.

The TFTs 112 each include a gate terminal 116, a source terminal 118,and a drain terminal 122, and are each coupled to one of the gate buslines 102, one of the data bus lines 104, and one of the pixelelectrodes 114. In the depicted embodiment, the gate terminal 116 ofeach TFT 112 is connected to one of the gate bus lines 102, the sourceterminal 118 of each TFT 112 is connected to one of the data bus lines104, and the drain terminal 122 of each TFT 112 is connected to one ofthe pixel electrodes 114. Thus, when the gate driver circuit 106supplies a gate select drive signal, via one or more gate bus lines 102,to one or more of the gate terminals 116, the associated TFTs 112 areturned on. As a result, the input signal voltages supplied from datadriver circuit 108 to the data bus lines 104 associated with theturned-on TFTs 112 are supplied to the associated pixel electrodes 114,thereby controlling light emission from the associated display pixel(not shown).

Turning now to FIG. 2, a cross section view of a portion of thebackplane 100, illustrating one of the TFTs 112 and one of the pixelelectrodes 114 in more detail, is shown and will be described. As shownin FIG. 2, the TFT 112 and pixel electrode 114 are each formed on aflexible substrate 202. The flexible substrate 202, which includes afirst surface 204 and a second surface 206, is preferably comprised of aflexible dielectric material such as, for example, plastic. In aparticular preferred embodiment, the flexible dielectric material ispolyethylene napthalate (PEN), though it will be appreciated that itcould be any one of numerous other flexible dielectric materials nowknown or developed in the future. No matter how the specific flexibledielectric material of which the flexible substrate 202 is formed,before the TFTs 112 or pixel electrodes 114 are formed on its firstsurface 204, the flexible substrate 202 is annealed. The annealedflexible substrate 202 is dimensionally more stable than a non-annealedflexible substrate. As a result, the previously mentioned thermal stressthat may arise from thermal expansion differences between the flexiblesubstrate 202, the TFT 112, and pixel electrode 114, are significantlyreduced. A more detailed description of a preferred substrate annealingprocess will be described further below.

The TFT 112 and pixel electrode 114, as was noted above, are formed onthe first surface 204 of the annealed flexible dielectric substrate 202.Preferably, before doing so, the first 204 and second 206 surfaces arecoated with a layer of a dielectric 208. In the depicted embodiment, theTFT 112 includes a gate electrode 212, a gate dielectric layer 214, anamorphous silicon (a-Si) layer 216, an inter-metal dielectric layer 218,a source contact 222, a drain contact 224, a source electrode 226, adrain electrode 228, a passivation layer 232, and a dielectric overcoatlayer 234. The gate electrode 212, which is formed of a conductivematerial, is electrically equivalent to, and functions as, the gateterminal 116 shown in FIG. 1. Similarly, the source 226 and drain 228electrode layers are each electrically equivalent to, and function as,the source 118 and drain 122 terminals, respectively, that areillustrated in FIG. 1.

As is generally known, the length (L) of that portion of the inter-metaldielectric layer 218 disposed between the source 222 and drain 224contacts defines the channel length of the TFT 112. Moreover, the a-Silayer 216 functions as the TFT channel, through which charge carrierstravel between the source contact 222 and drain contact 224. The source222 and drain contacts 224, as will be described in more detail furtherbelow, are each preferably formed from a contact enhancement layer 236and a barrier layer 238. The contact enhancement layer 236 improves TFTperformance by, for example, reducing the threshold voltage andincreasing the sub-threshold slope, and the barrier layer 238 functionsas a stable metallic conductive layer and forming an ohmic contact withand protecting the underlying reactive contact enhancement layer 236.

The passivation layer 232 and the dielectric overcoat layer 234 areformed over the TFT 112 and portions of the pixel electrode 114 toprovide passivation and/or protection of these devices. Morespecifically, in the depicted embodiment it is seen that the passivationlayer 232 is formed over the TFT 112, and the dielectric overcoat layer234 is formed over the passivation layer 232 and a portion of the pixelelectrode 114.

As FIG. 2 also shows, in the depicted embodiment the pixel electrode 114is electrically coupled to the drain electrode 228 via an interconnect240. The interconnect 240 includes a conductor 242, an interconnectcontact 244, a pixel electrode contact 246, and a portion of theinter-metal dielectric layer 218. The interconnect conductor 242, aswill be described in more detail further below, is preferably formed atthe same time, of the same material, and with the same thickness as thegate electrode 212. In addition, as will also be described in moredetail further below, the interconnect contact 244 and the pixelelectrode contact 246, are both formed at the same time, of the samematerial, and with the same thicknesses as the source 222 and drain 224contacts.

Having described an embodiment of a display backplane 100 from astructural standpoint, a particular preferred process of forming thedescribed backplane 100 will now be described. In doing so referenceshould be made, as appropriate, to FIGS. 3-11. It will be appreciatedthat, for clarity and ease of explanation, the process will be depictedand described using a simplified cross section view, similar to thatshown in FIG. 2. It will additionally be appreciated that although themethod is, for convenience, described using a particular order of steps,the method could also be performed in a different order or usingdifferent types of steps than what is described below. Moreover,although the method is described with respect to a single TFT 112, asingle pixel electrode 114, and a single interconnect 240, it will beappreciated that a plurality of TFTs 112, pixel electrodes 114, andinterconnects 240 may be formed on the same substrate 202.

With the above background in mind, and with reference first to FIG. 3,it is seen that the starting material for the backplane 100 is thesubstrate 202. As was noted above, the substrate 202 is preferablyformed of a flexible dielectric material, and is annealed at or near itsmaximum processable temperature to improve its dimensional stabilitythroughout the remaining process steps. In the depicted embodiment, inwhich the substrate 202 is formed of PEN, the substrate is annealed inan environment having a temperature of about 180° C. and a vacuum ofabout 1 milliTorr (mTorr) for about 16 hours. It will be appreciatedthat this temperature-pressure-time profile is merely exemplary, andthat it may vary depending, for example, on the particular flexibledielectric material used for the substrate 202. However, this particulartemperature-pressure-time profile for a PEN substrate results in lessthan 25 ppm shrinkage during the remaining process steps.

Before proceeding further, it is noted that the subsequent process stepsinclude various film deposition and photolithography processes. Thus;although not depicted, it will be appreciated that during the subsequentfilm deposition processes, the outer periphery of the flexible substrate202 (e.g., about 0.1″ from the substrate edge) is held with a pictureframe type fixture to hold the substrate 202 substantially flat duringfilm deposition. Moreover, though also not depicted, during thephotolithography processes the substrate 202 is held flat either by useof a vacuum chuck or by temporarily attaching the substrate 202 to aglass substrate (not shown) with a surfactant, such as a thin layer ofwater, between the glass and the substrate 202. In addition, though alsonot depicted, while the substrate 202 is relatively dimensionally stableafter annealing and barrier coating, in between process steps, thesubstrate 202 is preferably stored in a moisture free environment suchas, for example, a nitrogen purged glove box. This is preferably done tominimize dimensional changes that could potentially occur due tomoisture absorption.

Returning once again to a description of the backplane formation method,and with reference now to FIG. 4, it is seen that after the annealingprocess, and before any of the thin-film processing steps, the annealedflexible dielectric substrate 202 is coated with the dielectric material208 on both its first 204 and second 206 sides. In the depictedembodiment, the dielectric 208 is SiNx that is deposited to a thicknessof about 3000 Å. Although the dielectric 208 may be deposited (orotherwise formed) using any one of numerous deposition (or formation)processes, in the depicted embodiment the dielectric material 208 isdeposited using a plasma enhanced chemical vapor deposition (PECVD)process.

Once the annealed flexible dielectric substrate 202 is coated with thedielectric 208, the thin-film processing steps begin. Initially, as isshown in FIG. 5, the gate electrode 212 and interconnect conductor 242are simultaneously formed on the substrate first surface 204, over thedielectric 208. Preferably, the gate electrode 212 and interconnectconductive material layer 242 are formed by depositing any one ofnumerous types of electrically conductive materials, which are now knownor may be developed in the future, to a suitable thickness. In thedepicted embodiment, the gate electrode 212 and interconnect conductor242 are formed by sputter depositing NiCr to a thickness of about 1500Å, and patterning and etching the deposited NiCr using conventionalphotolithography techniques, such as an etch-back or a lift-offphotolithography technique, both of which are described in more detailfurther below. No matter the specific photolithography technique that isused, upon completion the photoresist layer (not illustrated) isstripped from the substrate 202. Though not shown in FIG. 5, it will beappreciated that the gate electrode 212 may be patterned to include agate bus line 102 as part of the same patterning process.

With continued reference to FIG. 5, it is seen that after the gateelectrode 212 and interconnect conductor 242 are formed, the gatedielectric layer 214 and the a-Si layer 216 are formed over the gateelectrode 212. In the depicted embodiment, the gate dielectric layer 214and the a-Si layer 216 are both deposited using a PECVD process at about160° C., and patterned and etched to the appropriate geometry. However,it will be appreciated that this is merely exemplary and that any one ofnumerous other processes may be used to form these layers 214, 216.Moreover, although the dielectric layer 214 may comprise any one ofnumerous dielectric materials of varying thicknesses, in the depictedembodiment the gate dielectric material is SiNx that is deposited to athickness of about 2500 Å. Similarly, the a-Si layer 216 may bedeposited to varying thicknesses, but in the depicted embodiment it isdeposited to a thickness of about 1000 Å.

The gate dielectric layer 214 and the a-Si layer 216 are, at least inthe depicted embodiment, sequentially deposited as part of a singledeposition process. However, it will be appreciated that this is merelyexemplary, and that these layers 214, 216 could instead be independentlydeposited via two separate deposition processes. Additionally, dependingon the particular design of the TFT 112, the gate dielectric layer 214and/or the a-Si layer 216 may be patterned and etched to define any oneof numerous device geometries. In the depicted embodiment, the gatedielectric layer 214 and a-Si layer 216 are aligned with one another,and together form an island that is centrally disposed over the gateelectrode 212.

Turning now to FIG. 6, it is seen that once the gate dielectric layer214 and a-Si layer 216 are formed, the inter-metal dielectric layer 218is then formed. The inter-metal dielectric layer 218 may comprise anyone of numerous dielectric materials, and may be formed (or deposited)to varying thicknesses. However, in the depicted embodiment, theinter-metal dielectric layer 218 comprises SiNx having a thickness ofabout 3000 Å. The inter-metal dielectric layer 218 may additionally beformed using any one of numerous know formation or depositiontechniques. In the depicted embodiment, however, the inter-metaldielectric layer 218 is formed using a technique that combines PECVD anda “partial” etch-back photolithography process. Before describing the“partial” etch-back photolithography process in more detail, forcompleteness a conventional etch-back photolithography process and aconventional lift-off photolithography process will each first bedescribed.

As is generally known, with a conventional etch-back photolithographyprocess, a material layer is deposited (or otherwise formed) on asurface of a substrate or other material layer. A layer of photoresistis then deposited over the deposited material layer. The photoresistlayer is then patterned using photolithography, which removes selectedportions of the photoresist layer and exposes portions of the underlyingmaterial layer. Then, using the remaining photoresist layer as a mask,the exposed portions of the underlying material layer are etched away.The remaining photoresist layer/mask is then removed.

With a conventional lift-off photolithography process, a layer ofphotoresist is first deposited on a surface. The photoresist layer isthen patterned using photolithography, which removes selected portionsof the photoresist layer and exposes portions of the underlying surface.The remaining photoresist layer then functions as a mask duringsubsequent material deposition. Thereafter, a material layer isdeposited on the photoresist layer/mask and on the exposed portions ofthe underlying surface. Once the material layer has been deposited, thephotoresist layer/mask and those portions of the material layerdeposited on the photoresist layer/mask are chemically “lifted off,”leaving the material layer on the exposed portions of the surface. Thus,with this photolithography technique the photoresist layer/mask issometimes referred to as a lift-off mask.

Returning once again to the description, it was noted above that theinter-metal dielectric layer 218 is formed using PECVD and a “partial”etch-back photolithography process. As used herein, this means that thephotoresist layer/mask (not shown in FIG. 6) is not removed after theinter-metal dielectric layer 218 is etched. Thus, following the etch ofthe deposited inter-metal dielectric layer 218, the photoresistlayer/mask remains in place and is used as a lift-off mask duringsubsequent photolithography processes, which are described in moredetail below. In any case, as is shown in FIG. 6, the photoresist layerthat is used during inter-metal dielectric layer deposition is patternedto include four contact via—a source contact via 602, a drain contactvia 604, an interconnection contact via 606, and a pixel electrodecontact via 608. As will now be described, the source contact 222, thedrain contact 224, the interconnection contact 244, and the pixelelectrode contact 246 are each formed in the source contact via 602, thedrain contact via 604, the interconnection contact via 606, and thepixel electrode contact via 608, respectively.

The source contact 222, the drain contact 224, the interconnectioncontact 244, and the pixel electrode contact 246, as was previouslynoted, each comprise a contact enhancement layer 236 and a barrier layer238. Referring now to FIG. 7, it is seen that the contact enhancementlayer 236 and barrier layer 238 are sequentially deposited over theinter-metal dielectric layer 218 using, for example, a thermalevaporation process and the photoresist layer/mask from the previousstep as a lift-off mask. In the depicted embodiment, the contactenhancement layer 236 and barrier layer 238 preferably comprise 700 Åthick layers of Yb and NiCr, respectively, though other materials andthickneses could be used. In any event, following the deposition (orformation) of these layers 236, 238, the lift-off mask is then removedusing any one of numerous known methods. In the depicted embodiment, thelift-off mask is removed in an ultrasonic acetone bath.

Once the source contact 222, the drain contact 224, the interconnectioncontact 244, and the pixel electrode contact 246 have each been formed,and as shown in FIG. 8, the source 226 and drain 228 electrodes areformed. To do so, a single layer of conductive material, such asaluminum, is deposited, patterned, and etched using any one of numerousmaterial deposition methods and photolithography techniques now known ordeveloped in the future. In the depicted embodiment, the aluminum layeris deposited using a sputtering technique, which is then patterned andetched using the above-described etch-back photolithography technique.No matter the specific techniques employed, it will be appreciated thatthe thickness to which the aluminum layer is deposited may vary, but inthe depicted embodiment the aluminum is deposited to a thickness ofabout 4000 Å. As FIG. 8 shows, after the photoresist has been patternedand the aluminum layer has been etched, the source electrode 226 iselectrically coupled to, and extends over, the source contact 222, andthe drain electrode 228 is electrically coupled to, and extends over andbetween, the drain contact 224 and the interconnection contact 244. Thepixel electrode contact 246, however, remains exposed.

After the source electrode 226 and drain electrode 228 have been formed,the passivation layer 232 is formed. As FIG. 9 shows, the passivationlayer 232, when formed, extends over the TFT 112 and a portion of theinterconnect 240. The passivation layer 232, like each of the previouslayers described herein, may comprise any one of numerous dielectricmaterials and may have any one of numerous thicknesses. Moreover, thepassivation layer 232 may be formed using any one of numerous materialdeposition methods and photolithography techniques now known ordeveloped in the future. In the depicted embodiment, the passivationlayer 232 comprises SiNx, and is deposited to a thickness of about 3600Å using PECVD. In addition, the passivation layer 232 is preferablypatterned and etched using the above-described “partial” etch-backphotolithography technique. Thus, after the deposited passivation layer232 has been etched, the photoresist layer/mask is not removed and isused as the lift-off mask for the subsequent photolithography process,which will now be described.

With continued reference to FIG. 9, it is seen that the photoresistlayer (not shown) used during passivation layer deposition is patternedto also include a pixel electrode contact via 902. Thus, the pixelelectrode contact 246 remains exposed. As a result, and with referencenow to FIG. 10, when the pixel electrode 114 is subsequently formed, itis electrically coupled to the pixel electrode contact 246. The pixelelectrode 114 is thus electrically coupled to the TFT drain electrode228 via the pixel electrode contact 246, the interconnect conductor 242,and the interconnect contact 244.

The pixel electrode 114 is formed by depositing a suitable materiallayer over the pixel electrode contact 246 and portions of thepassivation layer 232 using, for example, a sputtering process and thephotoresist layer/mask from the previous step as the lift-off mask. Thepixel electrode 114 may comprise any one of numerous suitable materialsnow known or developed in the future, and may be deposited to any one ofnumerous suitable thicknesses. In the depicted embodiment, the pixelelectrode 114 comprises indium-tin-oxide (ITO), and is deposited to athickness of about 1000 Å. Following the deposition (or formation) ofthe pixel electrode 114, the lift-off mask is removed in an ultrasonicacetone bath, though it will be appreciated that it could be removedusing any one of numerous other methods now known or developed in thefuture.

After the pixel electrode 114 is formed, the dielectric overcoat layer234 is formed. To do so, a layer of dielectric material is deposited,patterned, and etched using any one of numerous material depositionmethods and photolithography techniques now known or developed in thefuture. In the depicted embodiment, the dielectric material layer isdeposited using a PE CVD technique, and the deposited dielectricmaterial layer is patterned and etched using the above-describedetch-back photolithography technique. No matter the specific techniquesemployed, the material and thickness of the dielectric layer may vary,but in the depicted embodiment the material comprises SiNx, and isdeposited to a thickness of about 3600 Å. As FIG. 11 shows, after thephotoresist has been patterned and the overcoat layer 234 has beenetched, a portion of the pixel electrode 114 remains uncovered.

The flexible backplane 100 manufactured using the above describedprocess is ready for additional display fabrication. For example, as isshown in FIG. 12, the flexible backplane 100 of FIG. 2 is integratedwith an organic light emitting diode (OLED) structure stack 1202, acathode layer 1204, and additional thin film encapsulation layers 1206and 1208 to complete the fabrication of a flexible active matrix OLEDdisplay with a bottom emission 1210 architecture. The OLED structurestack 1202 is preferably fabricated using well known inkjet printingtechniques or masked vacuum evaporation techniques for fabricatingeither polymer OLED device structures or small molecule OLED devicestructures on the active matrix backplane 100. The cathode layer 1204 ispreferably a low work function cathode material that is preferablydeposited via any one of numerous thermal evaporation techniques. Thethin film encapsulation layers 1206 and 1208 may be deposited using anyof numerous known techniques such as CVD, sputtering, atomic layerdeposition, and may comprise any one of numerous appropriate barriermaterials that prevent moisture and oxygen ingression, to therebyenhance OLED lifetime. It will be appreciated that the active matrixbackplane 100 of FIG. 2 may also be used to fabricate flexible OLEDdisplays with top emission OLED architectures and other reflective,transmissive flexible displays using electrophoretic or liquid crystaldisplay media.

It will be appreciated that the above method of forming and electricallyinterconnecting a TFT 112 and pixel electrode 114 on a flexibledielectric substrate 202 is merely exemplary, and that the TFT 112 andpixel electrode 114 could be electrically interconnected without usingthe interconnect 240. For example, in an alternative embodiment shown inFIG. 13, the TFT 112 and pixel electrode 114 are electricallyinterconnected by forming a pixel electrode contact 1302 directly on thedrain electrode 228.

The flexible backplane 100 manufactured according to the methoddescribed herein provides enhanced dimensional stability, therebysubstantially eliminating potential layer to layer misalignment andminimizing thermal stresses that may arise from mismatches in thecoefficients of thermal expansion (CTE) between the substrate anddeposited material layers. The described method additionally minimizesor eliminates curling and warping of the substrate, which may occurduring manufacturing.

While at least one exemplary embodiment has been presented in theforegoing detailed description of the invention, it should beappreciated that a vast number of variations exist. It should also beappreciated that the exemplary embodiment or exemplary embodiments areonly examples, and are not intended to limit the scope, applicability,or configuration of the invention in any way. Rather, the foregoingdetailed description will provide those skilled in the art with aconvenient road map for implementing an exemplary embodiment of theinvention. It being understood that various changes may be made in thefunction and arrangement of elements described in an exemplaryembodiment without departing from the scope of the invention as setforth in the appended claims.

1. A method of forming an active matrix display backplane on a flexibledielectric substrate, comprising the steps of: forming a gate layer on asurface of the flexible dielectric substrate; forming a gate dielectriclayer over the gate layer; forming an amorphous silicon (a-Si) layerover at least a portion of the gate dielectric layer; forming aninter-metal dielectric layer over the a-Si layer; selectively removingportions of the intermetallic dielectric layer to thereby expose atleast a source contact region and a drain contact region on the a-Silayer; forming a source contact in the source contact region; andforming a drain contact in the drain contact region.
 2. The method ofclaim 1, further comprising: annealing the flexible dielectricsubstrate.
 3. The method of claim 2, wherein the step of annealing theflexible dielectric substrate comprises the steps of: heating theflexible dielectric substrate in an environment having a temperature ofabout 180° C. and a vacuum of about 1 milliTorr (mTorr) for about 16hours.
 4. The method of claim 1, wherein the flexible dielectricsubstrate comprises polyethylene naphthalate (PEN).
 5. The method ofclaim 1, further comprising: forming a layer of silicon nitride (SiNx)dielectric barrier layer on the surface of the flexible dielectricsubstrate.
 6. The method of claim 5, wherein the layer of SiNx is about3000 Å in thickness.
 7. The method of claim 6, wherein the step offorming the layer of SiNx comprises: depositing the SiNx on the surfaceof the flexible dielectric substrate using a plasma etch chemical vapordeposition (PECVD) processs.
 8. The method of claim 1, wherein: the gatelayer comprises nickel-chromium (NiCr); and the gate dielectric layercomprises silicon-nitride (SiNx).
 9. The method of claim 8, wherein thestep of forming the gate layer comprises: sputter depositing the NiCrover the deposited gate dielectric layer to a thickness in the range ofabout 1200 Å to about 1500 Å; and patterning and etching the gate layervia a photolithography process.
 10. The method of claim 8, wherein thestep of forming the gate dielectric layer comprises depositing the gatedielectric layer over at least the gate layer via a PECVD process. 11.The method of claim 10, wherein: the gate dielectric layer comprisessilicon-nitride (SiNx); and the SiNx gate dielectric layer is depositedto a thickness of about 2500 Å.
 12. The method of claim 11, wherein thestep of forming the a-Si layer comprises the step of: depositing thea-Si to a thickness of about 1000 Å via a PECVD process, wherein thegate dielectric layer and the a-Si layer are deposited sequentially tothereby form a SiNx/a-Si layer.
 13. The method of claim 12, furthercomprising patterning and etching the SiNx/a-Si layer.
 14. The method ofclaim 1, wherein the step of forming the inter-metal dielectric layercomprises: depositing a layer of SiNx to a thickness of about 3000 Å viaa PECVD process; depositing a photresist layer on the SiNx layer;patterning the photoresist layer to form a mask; and etching the SiNxinter-metal dielectric layer to thereby selectively remove portionsthereof and expose the source contact region and the drain contactregion on the a-Si layer.
 15. The method of claim 14, wherein the stepof forming the source contact and the drain contact comprises:depositing a contact enhancement layer on at least a portion of thephotoresist layer, the source contact region, and the drain contactregion; and lifting off the photoresist layer.
 16. The method of claim15, wherein the contact enhancement layer comprises ytterbium (Yb)deposited to a thickness of about 700 Å.
 17. The method of claim 15,wherein the contact enhancement layer comprises phosphorous doped n+a-Sideposited to a thickness of about 500 Å.
 18. The method of claim 16,further comprising: depositing a barrier layer on at least a portion ofthe contact enhancement layer, before lifting off the photoresist layer.19. The method of claim 18, wherein the barrier layer comprises NiCrdeposited to a thickness of about 700 Å.
 20. The method of claim 1,further comprising: forming a layer of conductive material over thesource and drain contacts; and selectively removing portions of theconductive material to thereby electrically insulate at least the sourceand drain electrodes from one another.
 21. The method of claim 1,further comprising: forming a pixel electrode on the surface of thesubstrate, the pixel electrode electrically coupled to the draincontact.
 22. The method of claim 21, wherein the pixel electrodecomprises indium-tin-oxide (ITO) having a thickness of about 1000 Å. 23.The method of claim 1, further comprising: forming an interconnectconductor on the surface of the substrate; forming an interconnectioncontact and a pixel electrode contact on the interconnect conductor; andforming a pixel electrode over at least the pixel electrode contact. 24.The method of claim 23, further comprising: forming a layer ofconductive material over the source contact, the drain contacts, theinterconnection contact, and the pixel electrode contact; andselectively removing portions of the conductive material to therebyelectrically insulate the source and drain electrodes from one anotherand electrically couple the drain contact to the interconnectioncontact.
 25. The method of claim 24, further comprising: forming a pixelelectrode over at least the pixel electrode contact, whereby the pixelelectrode is electrically coupled to the drain electrode via theinterconnect conductor, the interconnection contact, and the conductivematerial.
 26. The method of claim 24, wherein the pixel electrode isexposed when the portions of the conductive material are selectivelyremoved, and wherein the method further comprises: forming a passivationlayer over the conductive material and the pixel electrode; depositing aphotresist layer on the passivation layer; patterning the photoresistlayer to form a mask; and etching the passivation layer to therebyselectively remove portions thereof and once again expose the pixelelectrode.
 27. The method of claim 26, further comprising: forming apixel electrode over the pixel electrode contact and a portion of thepassivation layer, whereby the pixel electrode is electrically coupledto the drain electrode via the interconnect conductor, theinterconnection contact, and the conductive material.
 28. A method ofelectrically interconnecting a thin-film-transistor and a pixelelectrode formed on a substrate, comprising the steps of: forming aconductive material layer on the substrate; forming an interconnectcontact and a pixel electrode contact on the conductive material layer;electrically coupling the TFT to the interconnect contact; andelectrically coupling the pixel electrode to the pixel electrodecontact.
 29. An active matrix display, comprising: an annealed flexibledielectric substrate having at least a first surface and a secondsurface; a thin-film-transistor (TFT) formed on the annealed flexibledielectric substrate first surface; a pixel electrode formed on theannealed flexible dielectric substrate first surface; and aninterconnect formed on the annealed flexible dielectric substrate, theinterconnect including a conductor having an interconnect contact and apixel electrode contact formed thereon, the interconnect contactelectrically coupled to the TFT, the pixel contact electrically coupledto the pixel electrode.
 30. The active matrix display of claim 29,further comprising: an organic light emitting diode (OLED) structureformed on the annealed flexible dielectric substrate first surface andelectrically coupled to the interconnect.
 31. The active matrix displayof claim 29, further comprising: an electrophoretic (EP) structureformed on the annealed flexible dielectric substrate first surface andelectrically coupled to the interconnect.
 32. The active matrix displayof claim 29, further comprising: a liquid crystal display (LCD)structure formed on the annealed flexible dielectric substrate firstsurface and electrically coupled to the interconnect.